1. Technical Field
The invention relates generally to the field of molecular biology and cancer. More specifically, the invention relates to microRNA mimics corresponding to the miR-15/107 family and related methods of using microRNA mimics to treat malignant pleural mesothelioma (MPM) by restoring the regulation of expression of target genes of the miR-15/107 family in MPM tumor cells.
2. Background
Malignant pleural mesothelioma is an almost invariably fatal cancer for which few treatments are available. New therapies are urgently needed, and dysregulated microRNA expression provides a source of novel therapeutic targets.
MicroRNAs are transcribed by RNA polymerase II (pol II) or RNA polymerase III (pol III). See Qi et al. (2006) Cellular & Molecular Immunology, Vol. 3: 411-19. They arise from initial transcripts, termed primary microRNA transcripts (pri-microRNAs), which generally are several thousand bases long. Pri-microRNAs are processed in the nucleus by the RNase Drosha into about 70- to about 100-nucleotide hairpin-shaped precursors (pre-microRNAs). Following transport, to the cytoplasm, the hairpin pre-microRNA is further processed by Dicer to produce a double-stranded mature microRNA. The mature microRNA strand is then incorporated into the RNA-induced silencing complex (RISC), where it associates with its target mRNAs by base-pair complementarity. In the relatively rare cases in which a microRNA base pairs perfectly with an mRNA target, it promotes mRNA degradation. More commonly, microRNAs form imperfect heterduplexes with target mRNAs, affecting either mRNA stability of inhibiting mRNA translation.
Multiple studies have profiled mRNA gene expression in MPM to identify potential targets, and more recently, microRNA expression profiles have been generated, initially for diagnostic purposes using samples derived from normal and tumor cell lines, MPM tumors and pooled normal pericardium, or MPM and lung cancer. They also have been generated for prognostic purposes, i.e., within MPM tumors of different classification. See, e.g., Busacca et al., Am. J. Respir. Cell. Mol. Biol. 42: 312-19 (2010). However, none have made an extensive comparison between MPM tumors and normal pleural tissue.
Further, while relatively easy to use in vitro, microRNA mimics typically suffer, in terms of in vivo efficacy, due to two problems: (1) poor activity (including low RISC incorporation and off-target effects) and (2) inefficient delivery (related to stability and specific/selective distribution to the site of action).
As mentioned, multiple studies have profiled gene expression in MPM. This has been with the aim of understanding the disease process as well as to identify potential targets. These studies have characterized a general upregulation of metabolic and cell cycle genes in MPM, with additional changes in apoptotic genes associated with an altered apoptotic response linked to resistance to chemotherapy. To date, these studies have yet to reveal the overarching mechanism of genetic control of the phenotypes common to MPM tumors. However, as microRNAs are considered global modulators of gene expression, downregulation of expression of microRNAs represent a potential explanation for the upregulation of families of genes (i.e., loss of microRNA expression causes target gene upregulation).